Electric storage devices such as rechargeable batteries and capacitors are rechargeable and reusable and thus widely used as power sources. In general, a large capacity electric storage device has a case for accommodating an electrode assembly and the electrode assembly is accommodated within the case. Extraction of electric power from the electrode assembly is performed through electrode terminals connected to a positive electrode and a negative electrode.
The case of a rechargeable battery generally has a structure that is provided with a metal case main body and a metal lid fixed to the case main body by welding. The case main body has a rectangular cylindrical shape with a closed end. Since the case main body is formed by drawing a metal plate, four corners of the case main body do not form right angles but, for example, have round corner portions of an arcuate cross-section. A peripheral portion of the bottom is also a corner portion. Therefore, there may be a space between end faces of the electrode assembly and inner surfaces of the case main body when the electrode assembly is of a laminated type that is composed of rectangular positive electrode sheets and negative electrode sheets alternately laminated with separators sandwiched therebetween.
When the laminated-type electrode assembly is accommodated within the case main body with such space existing, a displacement between layers (between the electrode sheets and the separators) occurs due to vibration under the circumstances where the rechargeable battery is used while mounted on the vehicle, and this leads to degradation of battery performance. Further, the electrode assembly is likely to be short-circuited with the case main body. In a structure in which the electrode assembly is inserted into the case main body in the laminating direction, the displacement between the layers of the electrode assembly easily occurs at the time of the insertion of the electrode assembly.
FIG. 17 illustrates a conventional sealed lead storage battery. The electrode assembly is accommodated in a case main body (battery container) 60 via a spacer 68 in this storage battery. A positive plate terminal portion 66 and a negative plate terminal portion 67 protrude from end portions on the same side of a plate group 65 in the electrode assembly. The case main body has a rectangular tubular shape with a closed end. The spacer 68 is in close contact with side surfaces of the plate group 65.